1. Field of the Invention
The invention relates to a mechanism for selectively adjusting the cutting height of a walk-behind mower deck.
2. Description of the Prior Art
The present invention relates to large walk-behind mowers having a rear powered portion or base unit with driven wheels to propel the mower forwardly. The powered portion pushes a frame that carries a mower deck for cutting vegetation. The front of the frame is typically supported by caster wheels. An operator walks behind the powered portion while manipulating controls to vary the speed and direction of the mowing vehicle. These large walk behind mowers are generally more maneuverable than rider mowers and are often used in commercial settings such as large corporate grounds and golf courses where mower maneuverability is advantageous.
Conventional mowers of this type often provide mechanisms for adjusting the height of the deck above the ground to vary the height of cut. One type of conventional mower provides washers or spacers that can be inserted between the frame and the caster wheels to raise the deck relative to the ground. These spacers can also be removed to lower the deck. The operator must lift the front portion of the vehicle to allow for the removal or insertion of spacers. Tools may be required when adjusting spacers. The operator must remove or insert spacers at the various caster wheel locations to keep the mower deck level.
Another type of conventional mower provides pin members or screws that are adjustable to vary the height of the deck. A vertical plate having a plurality of openings is fixed to the deck and abuts a vertical plate fixed to the frame that also defines at least one opening. The pin member is held within one of the openings in the deck plate and the opening in the frame plate to hold the deck at a fixed height above the ground. The height of the deck can be adjusted by removing the pin, raising or lowering the deck, and placing the pin through the frame plate opening and a different opening in the deck plate. The deck height adjustment operation may not require the use of any tools, but does require the operator to physically lift the deck. The operator must change the pin positioning at various locations around the vehicle to keep the deck level. Also, this type of mower does not allow for infinite or fine adjustment of the deck height, since the openings are defined at particular locations.
Many mowing vehicles on which an operator rides provide front mounted mower decks whose height can be adjusted. Some of these rider mowers provide a system of spacers or pins as mentioned above.
Another type of rider mower provides a front mounted deck whose height is adjusted when the operator turns a crank handle. Push arms pinned to the front of the vehicle extend forwardly and are pinned to the top of the deck. The push arms act to push the deck forward during operation. Wheels coupled with the front of the deck hold the deck above the ground. The pin connections define an axis transverse to the direction of travel of the vehicle and about which the push arms and deck can pivot. Therefore, as the deck encounters irregular ground conditions, the pin connections allow the deck to pivot upwardly or downwardly with respect to the vehicle in order to ride over the ground irregularity. A crank handle operatively coupled to a transversely extending shaft is engagable by the operator to vary the deck height. The shaft is coupled with a four-bar linkage that extends between the deck and the front caster wheels, such that as the shaft rotates due to turning of the crank handle the height of the deck is changed. The push arms swing upwardly or downwardly, respectively, about the pin connection to the vehicle, as the deck is raised or lowered. A bell crank serves to link the shaft with the rear of the deck, and is pivotally carried by a bar fixed between the push arms. As the shaft pivots in response to the crank being turned, the bell crank will pivot to raise or lower the rear of the deck. Since the bell crank is carried by the push arms via the bar, the entire bell crank rises and falls with the push arms as the deck height is adjusted. The rising and falling of the bell crank also acts to raise and lower the rear portion of the deck. The vertical movement of the bell crank with the push arms therefore produces a portion of the total vertical movement of the rear of the deck during adjustment. The remaining portion of the movement of the rear of the deck is caused by the pivoting of the bell crank as the shaft rotates. Since the pivoting of the bell crank need only move the rear of the deck a portion of the total distance desired, the size and geometry of the bell crank is reduced and the mechanism's compactness and economy of manufacture is therefore improved.
However, the riding mower described above is not readily adaptable for use on a walk-behind mower. Rider mowers are multi-wheeled vehicles that remain upright regardless of whether a mower deck is attached. The powered units of large walk-behind mowers have only two wheels and rely on their connection with the front frame, deck, and front caster wheels to remain upright. The push arms of the rider mower are pinned to the multi-wheeled rear portion. Simply connecting the rider mower deck mechanism to the rear powered portion of the walk-behind mower via pin connections with the push arms would not serve to maintain the rear portion in an upright position. Rather, the rear portion would fall backwardly by rotating about the pin connection with the push arms. Furthermore, disadvantages exist in merely making the pin connection of the rider mowers rigid to adapt the rider's height adjustment mechanism for use with the walk-behind power unit. The push arms would still rise and fall as the front deck height is adjusted, which would cause the power unit to pivot about the drive wheels. Therefore, the operator handles fixed with the power unit would swing upwardly and downwardly about the drive wheels as the deck height is adjusted. It would be disadvantageous for the operator handles to be at various different heights, some of which may be uncomfortable for the operator, as the deck is adjusted.
It would be desirable to provide a powered walk behind mower with a mechanism for adjusting the height of the mower deck from a single station such that the deck remains generally level regardless of the height the operator selects. It would also be desirable for the operator to be able to infinitely adjust the height of the deck without the use of tools. In addition, such a mower should be compact such that the deck can fit beneath obstructions such as fences and bushes to facilitate trimming operations. It would also be desirable for such a mower to possess an anti-scalp feature such that the rear portion of the deck can rise up over irregular ground conditions.